Droplet ejection apparatus and method of cleaning the same

Abstract

A droplet ejection apparatus includes: a number of droplet ejection units each of which has a nozzle connected to a liquid chamber and an actuator for expelling droplets of a process liquid; a cleaning station; and a control system arranged to control a relative movement of the droplet ejection units and the cleaning station and to immerse the nozzles into a cleaning liquid, wherein a heater is provided for heating the droplet ejection units, and the control system is adapted to activate the heater when the droplet ejection units and the cleaning station are moved or have been moved towards one another, and to deactivate the heater to allow the droplet ejection units to cool down while the nozzles are immersed in the cleaning liquid.

The invention claimed is: 
     
       1. A droplet ejection apparatus comprising: a number of droplet ejection units each of which has a nozzle connected to a liquid chamber and an actuator for expelling droplets of a process liquid; a cleaning station; and a control system configured to control a relative movement of the droplet ejection units and the cleaning station and to immerse the nozzles into a cleaning liquid,
 wherein a heater is provided for heating the droplet ejection units, and the control system is further configured to activate the heater when the droplet ejection units and the cleaning station are moved or have been moved towards one another, and to deactivate the heater to allow the droplet ejection units to cool down while the nozzles are immersed in the cleaning liquid. 
 
     
     
       2. The apparatus according  claim 1 , wherein the droplet ejection units are mounted on a movable carriage. 
     
     
       3. The apparatus according  claim 1 , configured as an ink jet printer with a print head having the droplet ejection units. 
     
     
       4. The apparatus according to  claim 1 , wherein the droplet ejection units are configured for operation with a process liquid that is solid or forms a gel at room temperature. 
     
     
       5. The apparatus according  claim 1 , wherein the cleaning station comprises an upwardly open basin that contains the cleaning liquid, and a lift mechanism is provided for lifting and lowering the droplet ejection units and the basin relative to one another for immersing the nozzles into the cleaning liquid. 
     
     
       6. A method of cleaning a droplet ejection apparatus that comprises a number of droplet ejection units each of which has a nozzle connected to a liquid chamber and an actuator for expelling droplets of a process liquid, and a cleaning station that stores a cleaning liquid, wherein the method comprises the steps of:
 heating the droplet ejection units to an elevated temperature that is higher than room temperature when the droplet ejection units and the cleaning station are moved or have been moved towards one another; 
 immersing the nozzles into the cleaning liquid; and 
 allowing the droplet ejection units to cool down while the nozzles are still immersed in the cleaning liquid. 
 
     
     
       7. The method according to  claim 6 , comprising a subsequent step of re-heating the droplet ejection units for squeezing the cleaning liquid out of the nozzles though thermal expansion of a medium that is contained in the liquid chambers. 
     
     
       8. The method according to  claim 7 , comprising several cycles of heating and cooling the droplet ejection units.